Process for making ammonium fluorides



se t'. 20,1927. ,7 8 J. w. PROCTOR PROCESS FOR MAKING AMMONIUM FLUORIDES Filed Jan. 5, 1925 HF GAS SOLUTION OF AMMONIUM BIFLQURIDE OR NEUTRAL FLUORIDE AND HF MOTHER LIQUOR COOLER MOTHER L\QUOH ENRICHED wn'n H F CRYSTALLIZING BOX RYSTALS 01 AMMONlUM 'BTFLOURDE OR NEUTRAL FLOUFUDE.

INVENTOR Mn/5s W. Pfioarop M TNESS ,w/wwmw l A TTORNE VS upward and any gas remaining at the end h through a lead pipe 27 which extends near- Patented] Sept. 20', 1927.

UNITED STATES JAMES WILLIAM rnocron, or- BELLE venison, PENNSYLVANIA, ASSIGNOB To GEN-j v ERAL CHEMICAL COMPANY, OF NEW YORK, N. Y., A CORPORATION 01 NEW YORK.

I "raocnss roa mxme' AMMONIUM FLUOBIDES.

Application filed January 5, 1923. Serial No. 610,818,

This invention relates to the making of ammonium fluorides, either the so-called normal or neutral ammonium fluoride ge nerally represented by the chemical formula NH F, or the acid fluoride (also called ammonium lei-fluoride) the formula of which is usualy given as NH,F.HF.

The object of my invention is to provide an efficient and readily controlled process which by a simple adjustment will yield either the neutral or the acid fluoride as the product of the operation.

A leading feature of my invention consists in using the mother liquor from a batch of final product as a vehicle for absorbing fresh quantities of hydrofluoric gas or vapor, and treating the result of such absorption with gaseous ammonia to make a further amount of the product. Crystallization is thereupon used to separate the resulting neutral or acid ammonium fluoride (one or the other being obtained by properly ad- 'usting the amount of gaseous ammonia in relation to the. hydrofluoric content of the mother liquor), from the mother liquor which is then used again as an absorbing vehicle for another quantity ofhydrofluoric acid.

The process is preferably carried out in apparatus of the type illustrated diagram-f hydrofluoric acid gas a by, means of a pipe 1, reaches the bottom of a second absorption tower 2, from the top of which the gas portion not absorbed in this second tower passes through a flue 3 to a. third absorption tower .4, in which it travels this third absorption passes out throug the exit flue 5 to the waste gas stack where 1t escapes to the atmosphere. The mother liquor is stored in a tank 6, the outlet of which is connected by a pipe 7 with another tank 8. From the latter the liquor is transferred, by the use of a suitable propelling device,.such as an air-lift 9, through a pipe 10 to the top of tower 4. The liquor collecting at the bottom of this tower flows througha pipe 11 back to the tank 8, that a circulation'takes place through the closed path 8, 10, 4, 11, 8. An amount of liquor corresponding to that entering the tank 8 through the pipe 7 ,passesout through an overflow 12 to a cooler 13 provided with a gas vent 14 leading to the lower portion of the absorption tower 2. A portion of the liquor in cooler 13 is withdrawn through a pipe 16 and is conveyed by the action of a pump or other suitable propelling device,

such as the air-lift 15*, to the upper portion of a splash-"box 17 from which it passes down througha distributor 18 to the top of the absorption tower 2. Thus a second portion of liquor circulatesthrough the closed path 13, 16, 17", 18, 2, 13, it being understood that there is a pipe 2 connecting the lower portion of tower 2 with the upper portion of cooler 13. Similarly, a pipe 2 enables the liquor at the lower portion of tower '2 to flow into a cooler '13 which also,

through a pipe 19, receives the overflow from cooler 13*. An air-lift 15 or equivalent device takes a portion of the liquor from the cooler 13, through a pipe 16,- to a splash box 17, from which such liquor passes to a distributor 18 and then to the top of absorption tower 2. Thus a thirdortion of liquor is circulated through the dlosed path 13, 16, 17, 18, 2, 13.

The two splash-boxes 17, 17 a are connected by an air-vent 20 communicating with they From the pipe 16 a branch or overflow 21 leads to a crystallizing and neutralizing tank 22, connected by a siphon 23- with another tank 24, from which, by means of an air-lift 25 or other suitable device, the mother liquor is conveyed through a pipe 26 to the storage tank 6.

i The neutraliz ng and crystallizing tank 22 receives gaseous ammonia (from a usual storage container or" cylinder, not shown) In making ammonium bifluoride according to my process, with the aid of the apparatus shown, the procedure may be as follows:

First, I produce an initial body of mother liquor with which to start the process. For this purpose, the proper amount of hydrofluoric acid solution of a high strength (56% HF is suitable) and at atmospheric temperature, is run into a lead-lined tankof suitable capacity (the tank 22 may be used), and ammonia, preferably in the anhydrous or gaseous state, is passed into such acid (say, through the lead pipe 27) until a sufficient amount of ammonia has been absorbed to form a solution which upon subsequent cooling to atmospheric temperature will deposit crystals of ammonium bifluoride. The heat evolved by the reaction between the ammonia and hydrofluoric acid raises the temperature of the solution, which is then cooled to atmospheric temperature I (as by water passed through the coil 29) whereby crys-.

tals of ammonium bifluoride are caused to be deposited. Crystallization should be as complete as possible in order to avoid subsequent crystallization of the mother liquor in other parts of the apparatus and consequent clogging of the circulation path. A centrifugal machine or other suitable means is employed to separate the mother liquor from the crystals, and such mother liquor is filled either directly into the storage tank 6, or into the tank 24 from which it is transferred to said storage tank by the air lift 25, or other suitable device. The mother liquor prepared as described above will contain about of ammonium bifluoride and a certain amount of uncombined hydrofluoric acid. The main operation may then be started.

Hydrofluoric acid gas (obtained by the ac tion of sulfuric acid on calcium fluoride in an ordinary hydrofluoric acid still or in any other suitable way) is introduced at 1 into the tower 2 and travels upward therein, meeting the stream of liquid discharged downwardly from the distributor 18. The gas then passes through the pipe 1 to the second tower 2, and passes upwardly therein, meeting the downward stream of liquid from the distributor 18". Finally the gas passes through the flue 3 to thetower 4 and upwardly through the latter to the exit flue 5, meeting the stream of liquid which is discharged downwardly through the said tower 4 from the pipe 10. As explained above, the liquid 'assin through the tower 4 circulates throng the c osed path 10,4, 11, 8, 10, this liquid being a portion of the mother liquor which has reached the tank 8 from the storage tank 6. An amount of mother liquor substantially equal to the amount entering tank 8 'throu h the pipe 7, is taken out of said tank 8 by t e overflow 12 and pases to the cooler 13.

a certain amount of mother liquor circulatesthrough the closed path 13 through the overflow 'the process is replaced when necessar 16, 17 18*, 2, 2", 13, as above described. An amount of mother liquor substantially equal to the amount entering the cooler 13 12, is Withdrawn through the overflow l9 and a certain amount of liquor circulates through the third closed pat-h 13, 16, 17, 18, 2, 2, 13, as above described. In this manner the ammonium bifluoride liquor is circulated over the towers 2, 2* and 4 until it has absorbed as much hydrofluoric acid as is practicable, preferably until the mother liquor is-substantially saturated with hydrofluoric acid; for instance until the total hydrofluoric acid content amounts to approximately from to The heat of absorption in the three towers is sufficient,- when the proper adjustments have vent crystallization in the circulating liquor, but is not suflicient to cause any substantial loss of ammonia-content. Finally, an amount of liquor substantially equal to that entering the cooler 13 through the overflow 19, is withdrawn continuously through the overflow pipe 21 into theneutralizing and crystallizing-tank 22. Here I add, through the pipe 27, the proper amount of ammonia, preferably in the anhydrous or gaseous state, to make ammonium bifluoride. Theamount required for this purpose is determined by an analysisof the iquor in the neutralizing tank 22. After adding the proper amount of ammonia, I allow the liquor to cool and to crystallize (the cooling action being obtained by means of the coil 29), and separate the crystals of ammonium bifluoride in any suitable manner. The mother liquor is siphoned oif through the pi e 23 into the tank 24, and this siphoning oft may be'sufiicient for separating the crystals from :the mother liquor. From the tank 24 the mother liquor passes to the storage tank 6 and from there again enters the circulation path in the manner described.

In this way, by having a sufl'icient number of neutralizing and crystallizing .vessels such as 22 available, I obtain continuous absorption of the hydrofluoric acid generated in the stills. Since the mother liquor contains at all times a substantial amount of dissolved ammonium bifluoride, I avoid the nuisance and loss caused by the evolution of fumes when ammonia is aqueous solution of hydrofluoric acid. The water which is lost in small amounts duriifig dllIiIKtlOH of the liquor in the neutrallzing' tan a I At no time during the process is evaporation of the liquor and ;the consequent consumption of fuel necessary since crystallization occurs on cooling the liquor after treating it with ammonia, and no substantial amount of ammonium bifluoride is lost, all

mother liquors being returned to the process into the cooler 13,

introduced into the strong been made, to prefor the absorption of hydrofluoric acid gases. The elimination of evaporation reduces the amount of apparatus required, as well as the amount of supervision, and shortens the time required for producing a given quantity of product.-

When'it is desired to make neutral ammonium fluoride instead of ammonium bifluoride, this is accomplished by simply changing the proportions of ammonia and hydrofluoric acid, that is to say, a greater amount of ammonia will be added at the neutralizing tank, in the proportion required for the formation of neutral ammonium fluoride. p

Various modifications may be made without departing from the nature of my invention as set forth in the appended claims. Thus, for example, while I have shown three towers for the successive absorption of hydrofluoric acid gas, their number might be varied, and evena single absorption step might be used in some cases and obviously. there are many other variations in detail which could be employed in the practice of the invention without departure from the essentials thereof. 1

Thus, for continuous operations, a mechanical crystallizer of any well known or approved type may be substituted for the specific crystallizer which is illustrated in the drawing and any changes or modifications of such type or character are included within the scope of the inventionand are intended to be covered by the claims.

I claim:

1. In the art of making an ammonium fluoride, that improvement which comprises exposing a gas containing hydrofluoric acid gas, to contact treatment with a liquor containing an ammonium fluoride, until such a solution of hydrofluoric acid in said liquor is obtained that, on subsequent addition of ammonia and cooling, an ammonium fluoride will crystallize from the mother liquor, treating the liquid product resulting from the said contact treatment between hydrofluoric acid gas and liquor, with ammonia to form an ammonium fluoride in the liquor, crystallizing out an ammonium fluoride, separating the said crystals from the mother liquor and using the mother liquor as the liquor of the first step.

2. In the art of making an ammonium fluoride, that improvement which comprises exposing a gas containing hydrofluoric acid gas, to counter-current contact treatment with a liquor containing an ammonium fluoride, until such a solution of hydrofluoric acid in said liquor is obtained that, on subsequent addition of ammonia and cooling, an ammonium fluoride will crystallize from the mother liquor, treating the liquid product resulting from the said counter-current contact treatment between hydrofluoric acid tals.

gas and liquor, with ammonia to form an ammonium fluoride in the liquor, cooling the, liquid to crystallize out an ammonium fluoride, separating the said crystals from .the mother liquor and using the mother liquor as the llquor of the first step.

fluoric acid gas to abstract substantially the whole of the hydrofluoric acid gas from said gas stream, treating the resulting liquor with ammonia under temperature conditions favorable to the crystallization of an ammonium fluoride from said liquor, separating the resultant crystals from the mother liquor and withdrawing the mother liquor for use as mother liquor of the first step in a repetition of the cycle of operations.

4. In the art of making an ammonium fluoride, the improvement which comprises supplying continuously mother liquor from a batch of finished ammonium fluoride product, circulating such liquor in counter-current contact with hydrofluoric acid gas to produce a solution of hydrofluoric acid in such mother liquor, withdrawing from such circulation a portion of said solution corresponding substantially to the amount of mother liquor supplied continuously, treating the portion thus withdrawn with ammonia, crystallizing out the ammonium fluoride obtained, and separating the mother liquor from the crystals.

5. In the art of making an ammonium I fluoride, theimprovement which comprises supplying continuously mother liquor from a batch of finished ammonium fluoride prod,- uct, circulating such liquor in contact with hydrofluoric acid gas to produce a solution of hydrofluoric acid in such mother liquor,

withdrawing from such circulation a portion of said solution correspondingsubstantially to the amount of mother liquor supplied continuousl cooling such withdrawn 7 portion and circu ating it in absorptive contact with hydrofluoric acid gas to strengthen the said solution in hydrofluoric acid con 1 tent, withdrawing from circulation a portion of the strengthened solution corresponding substantially to the amount of mother liquor supplied continuously, treating the portion thus withdrawn with ammonia, crystallizing out the ammonium fluoride obtained, and separating the mother liquor from the ,crys-' '6. In the art of making an ammonium fluoride, the improvement which comprises treating mother liquor from a batch of finished ammonium uoride product with hydrofluoric acid to produce a solution of hydrofluoric acid in such mother liquor, treat-f ing the resulting liquid withammonia, crys tallizing out at atmospheric temperature 'the ammonium fluoride obtained, and separating the motherliquor from the crystals.

7. In the art of making an ammonium fluoride, the improvement which comprises absorbing substantially all of the hydrofluoric acid present in a gas with a fresh unsaturated solution of mother liquor before said gas is permitted to go to the waste stack, using the resulting mother liquor to treat the said hydrofluoric acid-bearing gas prior to the aforesaid operation, until the motherliquor is substantially saturated with respect to hydrofluoric acid, and withdrawing said saturated mother liquor for a crys- 'tallizing operation.

8. In the art of making an ammonium fluoride, the improvement which comprises continuously feeding a hydrofluoric acid gas into an absorption system at a point where treated gas has substantially all of its hydro-- fluoric gas removed therefrom, permitting said gas to escape into the atmosphere after employing a counter-current absorption system of a plurality of stages in which a mother'liquor of ammonium fluoride is used for absorbing hydrofluoric acid from a gas bearing said acid, the fresh unsaturated mother liquor being introduced into the system at a point immediately prior to the waste gas stack and the hydrofluoric acid bearing gas at a point adjacent to the outlet for mother liquor. saturated withsaid acid. In testimony whereof I have hereunto set my hand.

JAMES WILLIAM PROCTOR. 

